Beginning with Colin Kaepernick last year, dozens of players have taken a knee during the Anthem to protest racial injustice. Kaepernick is now a free agent, and has filed a grievance against the owners, alleging they colluded to keep him from being signed.

Last week, Commissioner Roger Goodell said the league needs to "move past this controversy" over the anthem. But he said, "Like many of our fans, we believe that everyone should stand for the National Anthem."

The protests got even more attention after President Trump denounced them during a campaign-style rally in Alabama in September. He said that any players who refused to stand should be fired.

"Wouldn't you love to see one of these NFL owners, when somebody disrespects our flag, to say, 'Get that son of a bitch off the field right now. Out! He's fired. He's fired,'" he said.

After Trump's attack, hundreds of players joined the protest, and the NFL promoted the message that it was unified.

Several owners released statements criticizing the president's comments and some locked arms with their players during the anthem.

Since that show of solidarity, the strain has only grown. Dallas Cowboys owner Jerry Jones said any player who "disrespects the flag" will not play.